very simple condition, actually - much like a residential deck, but with
precast plank and foolishly large piers. The piers may drop to 16"
sonotube when the client gets the estimate on the stone-clad, pyramidal
piers. I suppose I could just encase the top of the helical pier in the
concrete pier and forgo the separate pile cap, but I'm concerned about
the potential for moment in the helical pier shaft if the installation
isn't perfectly centered under the post above. 3-4" off with a 40+kip
load would likely exceed the capacity of the shaft. Most of the contact
I've had with these types of piles is either as shoring of existing
buildings with light loads (maybe 10k), or using multiples under caps
for capacity reasons.
Jordan
David Maynard wrote:
> John Pack, PE, of IMR, Inc. out of Denver, CO, has done extensive studies
> with AB Chance Helical Piers. If you do an installation torque of 10,000
> ft. lbs, you could get an Ultimate Capacity of the pier to be 100 kips.
> With a factor of safety of 2.0, that's a 50 kips design capacity. If they
> have the materials to build a 50 kip (design capacity, 100 kip ultimate
> capacity) helical pier (heavier shaft, several helix flights, etc., then you
> can use a local helical pier for this particular load and isolate it from
> the rest of the foundation.
>
> Otherwise, with the spread that you have, you would have to design the
> foundation as a concrete beam between these two piers. I might not have a
> clear understanding of your problem. If you had a diagram to share, I might
> have more information.
>
> Dave Maynard
> Gillette, WY
>
>
> -----Original Message-----
> From: Jordan Truesdell, PE [mailto:seaint2@truesdellengineering.com]
> Sent: Wednesday, June 11, 2008 9:28 AM
> To: seaint@seaint.org
> Subject: 1 or 2 piles under a cap
>
> Does anyone have a rule of thumb for using less than 3 piles (helicals,
> in my case) under a pile cap? I've got a condition where I have some
> lightly loaded pile caps - about 45k - but their supporting pyramidal
> piers which have a 40" square base. The tops of the piers will support
> a beam line and concrete plank, so there's no lateral loads. The piers
> are 16-20' apart and are in a (roughly) straight line, so I can't
> efficiently combine multiple piers under a single footing.
>
>
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